after the death of Levi's squad, the village people were whispering and this is as IF Levi was not as stable as he actually is. In this, the death of his team gets to him and Eren, feeling guilty and thinking it was his fault, decides to stay by Heichou's side and do anything he can to help. Levi is losing his mind however and is becoming heartless due to the shattered feelings inside and ends up taking advantage of Eren's loyalty in many different ways--sexually included. Despite this, Eren is in love with Levi and believes that this is love and that Levi is simply trying to cope. But he does eventually realize and question Levi's actual feelings towards him. Was he just being used or did Heichou really like him? Levi is abusive, teasing and very sadistic towards Eren and soon, the boy forces himself to believe it, even if he doesn't want to. He wants to believe Levi loves him, but he isn't sure. One thing he is sure of, their relationship was becoming dangerous and it needed to end. Still guilty, Eren cuts the ties with Levi.
The last part, Levi is depressed. He didn't realize what he had until he lost it. He cuts himself as he's playing the piano. As his "younger self" is being choked by an unidentifiable person, represents him trying to off himself; commit suicide.
In the end, Eren visits Levi in the infirmary.
{Idea inspired by a video- I sadly lost the link to it so if you find it please let me know!}